Radio link failure detection procedures in long term evolution uplink and downlink and apparatus therefor

ABSTRACT

A method and apparatus for detecting a radio link (RL) failure for uplink (UL) and downlink (DL) in a long term evolution (LTE) wireless communication system including at least one wireless transmit/receive unit (WTRU) and at least one evolved Node-B (eNodeB) are disclosed. A determination is made as to whether an RL has an in-synchronization status or an out-of-synchronization status. An RL failure is declared if an out-of-synchronization status is detected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/742,847, filed May 1, 2007, currently pending, which claims thebenefit of U.S. Provisional Patent Application No. 60/798,119, filed May5, 2006, the entire contents of both applications being herebyincorporated by reference herein, for all purposes.

FIELD OF INVENTION

The present invention is related to wireless communication methods andapparatus having a medium access control (MAC) layer specificallydesigned for wireless communication systems such as long term evolution(LTE) systems. More particularly, the present invention is related tocriteria and procedures in LTE MAC for detecting radio link (RL) failurein both uplink (UL) and downlink (DL) directions when there is noexisting dedicated channel in the LTE system.

BACKGROUND

An objective of Evolved Universal Terrestrial Radio Access (E-UTRA) andUniversal Terrestrial Radio Access Network (UTRAN) is to provide a radioaccess network featuring a high-data-rate, low-latency, packet-optimizedsystem with improved system capacity and coverage. In order to achievethis, the inventors have observed that evolution of the radio interfaceas well as the radio network architecture is needed. For example,instead of using code division multiple access (CDMA), which iscurrently used in third generation partnership project (3GPP),orthogonal frequency division multiple access (OFDMA) and frequencydivision multiple access (FDMA) are proposed air interface technologiesto be used in the DL and UL transmissions, respectively, for E-UTRAUTRAN.

Signaling radio bearers (SRB) are used to maintain the connectionbetween a wireless transmit/receive unit (WTRU) and a network bytransmitting important information, such as a handover message from thenetwork, e.g., transmitting such information in a dedicated channel(DCH) cell level (Cell_DCH) state in 3GPP. In current 3GPP standards,the SRBs are mapped to dedicated transport channels (TrCHs), (i.e.,DCHs), which are then mapped to dedicated physical channels. Thededicated physical channels are comprised of dedicated physical controlchannels (DPCCHs) and dedicated physical data channels (DPDCHs).

In order to detect the failure of the SRBs, and to take necessarymeasures following the failure, certain criteria and procedures need tobe designed. This is known as radio link (RL) failure detection. In3GPP, there are two quantities to be estimated for reportingin-synchronization status and out-of-synchronization status. Onequantity is a DPCCH quality, and the other quantity is a cyclicredundancy check (CRC) results on the received transport blocks to whichthe SRBs are mapped.

A Node-B or WTRU should estimate the DPCCH quantities and calculate theCRC in parallel in order to check if the certain criteria are fulfilledfor reporting either the in-synchronization status or theout-of-synchronization status. The criteria identified may be onlyapplicable when SRBs are mapped to shared channels, and their associatedcontrol channels are identified for RL failure conditions.

Dedicated physical channel availability is indicated by the physicallayer to higher layers with a physical channel in-synchronization statusindicator or a physical channel out-of-synchronization status indicator.A RL is said to be in synchronization, (in-sync), if it is available tosuccessfully receive data. Otherwise, the RL is said to be in failure,i.e. when it is out of synchronization (out-of-sync). In the current3GPP standard, it is the responsibility of physical layer to monitor thededicated physical channels, determine the in-sync and out-of-syncstatus of every radio frame, and report the results to the radioresource control (RRC) layer using the primitives physical layer controlmessage in-synchronization indicator (CPHY-in-sync-IND) and physicallayer control message out-of-synchronization indicator(CPHY-out-of-sync-IND). The RRC layer will declare the physical channelestablishment or failure, or RL failure, whenever appropriate based onthese indications and associated timers and counters.

In 3GPP, high speed DL packet access (HSDPA) and high speed UL packetaccess (HSUPA) protocols utilize high speed shared channels primarilyfor services that do not require continuous channel allocations. Suchchannels utilize fast physical and MAC layer signaling between Node-Bsand WTRUs for channel assignment and hybrid automatic repeat request(H-ARQ) for efficient and fast recovery of failed transmissions.

When the service supported by a cellular system is mapped to sharedchannels, the inventors have recognized that the use of dedicatedchannels to support SRBs is inefficient. This is because the traffic maynot be continuous. Thus, it would be desirable to use shared channels tosupport the SRBs in HSDPA and HSUPA.

SUMMARY

The present invention relates to methods and apparatus for implementingnew criteria and procedures for radio link (RL) failure detection inwireless communication systems (e.g., LTE systems). Preferably theinvention is implemented for both UL and DL directions by exploiting anew channel structure and characteristics for LTE. Preferably, a sharedchannel is used to transmit bursty SRBs.

Embodiments contemplate a wireless transmit/receive unit (WTRU) that maybe configured to determine a radio link (RL) synchronization status. TheWTRU may be configured to determine a quality of a downlink (DL) commonshared control physical channel communicated in a channel structurecorresponding to a long-term evolution (LTE) compatible network. TheWTRU may also be configured to compare the quality to a predeterminedthreshold to determine the RL synchronization status, based at least inpart, on the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of an LTE configured in accordance with thepresent invention.

FIG. 2A is a signaling diagram depicting a DL RL failure detectionprocedure in accordance with the present invention.

FIG. 2B is a flow diagram of a method for detecting DL RL failure.

FIG. 3A is a signaling diagram depicting a UL RL failure detectionprocedure in accordance with the present invention.

FIG. 3B is a flow diagram of a method for detecting UL RL failure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “evolved Node-B (eNodeB)”includes but is not limited to a base station, a site controller, anaccess point (AP), or any other type of interfacing device capable ofoperating in a wireless environment.

When referred to hereafter, the terminology “thin channel” is anon-contention-based channel that is periodically and/or temporarilyallocated to a particular WTRU. A thin channel may be dynamicallyallocated, (i.e., switched on an off), when needed to maintain radiolink status and provide other control signaling. The other controlsignaling may include synchronization bursts for maintaining timingadvance, scheduling requests, scheduling allocations, or any otherchannel associated control signaling.

In an LTE system, only shared physical channels are used fortransmission for both DL and UL. Thus, in addition to data traffic, bothreal time, (i.e., voice over Internet Protocol (VoIP)), and non-realtime, (i.e., web browsing), a control message mapped to SRBs istransmitted through a shared physical channel. This is a distinctionfrom systems that transmit control messages in a dedicated channel(DCH).

Ensuring WTRU and UTRAN detection of SRB loss and recovery with respectto a shared channel presents a problem which is different than when adedicated channel is used. In the absence of a dedicated channel,burstiness in offered traffic load may cause an undetected SRB failure.This problem exists for both DL and UL.

An LTE system 100 including a WTRU 105 and an evolved Node-B (eNodeB)110 which addresses this problem in accordance with the presentinvention is illustrated in FIG. 1. The WTRU 105 and the evolved Node-B(eNodeB) 110 are preferably configured with a hierarchy of processingcomponents including a physical layer component, a MAC layer componentand higher layer components. The physical layer component is preferablyconfigured to physically transmit and receive wireless signals. The MAClayer component is preferably configured to provide control functionsfor the physical layer, and to act as a conduit for data and othersignaling from higher layers for formatting and transmission by thephysical layer, and to pass data and other signaling received by thephysical layer to the higher layer components.

RL Failure Detection in DL—Procedures at the WTRU

As shown in FIG. 1, for DL transmission, scheduling information istransmitted on a DL shared control channel 115 from the eNodeB 110 tothe WTRU 105. From the control signaling received on the DL sharedcontrol channel 115, the WTRU 105 receives information as to thephysical resources that are allocated. A DL shared data channel 120 isused to transmit data from the eNodeB 110 that is received by the WTRU105 via allocated physical resources. The WTRU 105 then transmits H-ARQfeedback 125 to the eNodeB 110, (i.e., positive acknowledgement(ACK)/negative acknowledgement (NACK)). The WTRU 105 also transmits achannel quality indication (CQI) 130 to the eNodeB 110 based on themeasurement and estimation of at least one DL reference channel 135 thatis transmitted from the eNodeB 110 and received by the WTRU 105.

The WTRU 105 continuously determines whether an in-synchronizationstatus or an out-of-synchronization status is detected, and reports theresults through a signaling message. A higher layer component isconfigured to preferably declare an RL failure based on appropriatecriteria and associated timers and counters, only when an out-ofsynchronization status is detected. Preferably, the MAC layer componentof the WTRU 105 is configured to determine whether an in-synchronizationstatus or an out-of-synchronization status is detected. Quantities usedfor estimation for the DL RL failure detection are discussed below andare preferably based on the characteristics of the LTE DL channelstructure.

To address resource sharing and allocation to the WTRU 105 in terms ofavailability of the traffic, new procedures have been devised based onnew criteria. By exploiting various shared channels and the informationcontained therein, the following preferred options of criteria are usedto declare DL RL failure at the WTRU 105. Preferably, a combination ofone or more criteria is selected from the following five preferredcategories for this purpose.

1) DL Channel Quality (sliding window average):

-   -   1a) whether CQI measured from a DL reference channel, e.g. from        a pilot or from a broadcast channel, and reported to the eNodeB        is below a specified threshold Q_(DL) _(—) _(CQI) within a        certain period (timer T_(DL) _(—) _(CQI));    -   1b) whether CQI from the eNodeB measured on UL reference        channels transmitted from WTRU is below a specified threshold        Q_(UL) _(—) _(CQI) within a certain period (timer T_(UL) _(—)        _(CQI)) or cannot be received on a regular basis; and    -   1c) a combination of CQI for both UL and DL.

2) DL Shared Control Channel

-   -   2a) whether quality of DL common shared control physical        channel, e.g. signal to interference ratio (SIR), energy per bit        per noise power spectral density (EbNo), CRC/block error rate        (BLER) (Q_(SC) _(—) _(DL) _(—) _(SIR), Q_(SC) _(—) _(DL) _(—)        _(BLER)), is below a certain threshold over a specified time        period (timers T_(SC) _(—) _(DL) _(—) _(SIR), T_(SC) _(—) _(DL)        _(—) _(BLER)); and    -   2b) whether quality of DL dedicated shared control physical        channel, e.g. SIR, EbNo, CRC/BLER, and the like (Q_(DC) _(—)        _(DL) _(—) _(SIR), Q_(DC) _(—) _(DL) _(—) _(BLER)), is below        certain threshold over a specified time period (T_(DC) _(—)        _(DL) _(—) _(SIR), T_(DC) _(—) _(DL) _(—) _(BLER)).

3) DL Shared Data Channel

-   -   3a) whether quality of DL data shared physical channel, e.g.        SIR, EbNo, CRC/BLER, and the like (Q_(SD) _(—) _(DL) _(—)        _(SIR), Q_(SD) _(—) _(DL) _(—) _(BLER)), is below certain        threshold over a specified time period (timers T_(D) _(—) _(DL)        _(—) _(SIR), T_(D) _(—) _(DL) _(—) _(BLER));    -   3b) whether an ACK/NACK ratio generated at WTRU and fed back in        UL for the DL data packets is below a specified threshold        (Q_(SD) _(—) _(DL) _(—) _(ACK));    -   3c) whether an ACK/NACK ratio fed back from the eNodeB for UL        data packets is below a specified threshold (Q_(SD) _(—) _(UL)        _(—) _(ACK)); and    -   3d) a combination of items 3b) and 3c).

4) UL Resource Grant

-   -   4a) whether allocated UL resource cannot guarantee the SRB bit        rate;    -   4b) whether there is a timeout following no response to        single/multiple resource requests (C_(UL) _(—) _(Request)) sent        over a uplink dedicated physical channel; and    -   4c) whether there is a timeout following no response to single        or multiple resource requests (R_(UL) _(—) _(Request)) sent over        a random access channel (RACH) in Active state.

5) A periodic DL Channel for DL Dedicated transmission

-   -   5a) whether quality of DL data shared physical channel, e.g.        SIR, EbNo, CRC/BLER, and the like, is below a certain threshold        over a specified time period (timers T_(D) _(—) _(DL) _(—)        _(SIR), T_(D) _(—) _(DL) _(—) _(BLER));    -   5b) whether an ACK/NACK ratio generated at WTRU for DL data        packets is below a specified threshold (Q_(DL) _(—) _(Dedi) _(—)        _(ACK));    -   5c) whether an ACK/NACK ratio provided as feedback from eNodeB        for UL data packets is below a specified threshold (Q_(UL) _(—)        _(Dedi) _(—) _(ACK));    -   5d) where a UL thin channel is used to probe, (i.e., “ping”),        for RL failure based on criteria similar to those used to        determine DL RL failure; and    -   5e) a combination of items 5b) and 5c)

The eNodeB 110 preferably selects a combination of the above quantitiesand parameters and the corresponding thresholds, timers, counters to beused for RL status detection and then transmits a selected configurationto the WTRU 105. The configuration signals to support the DL RL failuredetection preferably include:

-   -   1) A combination of estimation quantities and parameters for RL        failure detection;    -   2) Specific timer duration for each quantity and parameter where        the RL failure timer configuration is preferably based on the        WTRU sensitivity; and    -   3) Specific counters for each quantity and parameter.

Once the WTRU 105 is configured with this information, it can begin theRL detection process. The signaling for DL RL failure detectionpreferably uses a DL RL failure indication. A high level procedure canbe implemented, preferably in an embodiment dealing with a “Keep Alive”(using thin channel) case or an embodiment dealing with a “Non-KeepAlive” (without using thin channel) case.

FIG. 2A is a signaling diagram depicting a DL RL failure detectionprocedure in a wireless communication including a WTRU 105 and an eNodeB110 in accordance with the present invention. As shown in FIG. 2A, a CQIis measured from a DL reference channel and is provided to the WTRU 105as feedback from the eNodeB 110. The DL RL failure detection may detectthe failure of a DL shared control channel, a DL shared data channel, aUL resource grant or a DL thin channel.

Generally, in accordance with the present invention, a high level DL RLdetection procedure is preferably implemented with the following steps:

-   -   1) A combination of estimation quantities are selected to serve        as the criteria for DL RL failure detection. The estimation        quantities are preferably a combination of criteria as described        above. Preferably, associated thresholds and timers are included        as described in above paragraphs individually along with the        estimation quantities. Preferably the configuration is        determined by the eNodeB 110 and signaled to the WTRU 105.    -   2) The WTRU 105 is preferably configured with the selected        combination of quantities and parameters before the start of the        detection procedure. Preferably, the MAC component of the WTRU        105 is provided with the ability to be selectively configurable        for this purpose.    -   3) The WTRU 105, preferably via its MAC component, then monitors        the selected combination of quantities and parameters. When the        configured estimation quantities do not meet selected thresholds        within a pre-configured time period, a DL RL failure is detected        and declared.    -   4) The WTRU 105 then signals the failure status to the eNodeB        110.    -   5) Actions for DL RL recovery are then taken, and the timers and        counters are reset for a new detection.

In accordance with a first embodiment of the present invention, a highlevel DL RL detection procedure for a keep alive channel scenario ofSRBs a pre-allocated DL thin channel is maintained. Where there is apre-allocated DL thin channel maintained for SRB, the channel quality ismeasured on a DL thin channel is preferably selected as a main quantityto estimate the quality for DL SRB transmission. Other estimationquantities are selected to serve as a complimentary approach to assistthe DL RL failure detection is selecting the combination of estimationquantities with which to configure the WTRU.

In accordance with a second embodiment of the present invention, a highlevel DL RL detection procedure for a non-keep alive channel scenario ofSRBs is implemented. In this case, there is no pre-allocated DL thinchannel for SRB service. Although there are other periodic DLreceptions, such as DL reference channels, that are not directly relatedto the DL SRB transmission. Accordingly, such other periodic DLreceptions are preferably only used in combination with other quantitieswhich preferably includes the shared data channel transmitting the DLSRBs.

FIG. 2B is a flow diagram of a method 200 for detecting DL RL failure.In step 205, the channel quality of a DL thin channel is measured ifthere is a pre-allocated DL thin channel maintained for an SRB toestimate the quality for DL SRB transmission. In step 210, quantitiesand parameters are configured for performing DL RL failure detectionwhich is then conducted in step 215. If a DL RL failure is detected anddeclared in step 215, a WTRU signals DL RL failure status to an eNodeBin step 220. The WTRU then performs necessary actions for DL RL recoveryin step 225 and the WTRU resets timers and counters for new RL failuredetection in step 230.

RL Failure Detection in UL—Procedures at the eNodeB

As shown in FIG. 1, for UL transmission, the scheduling information isalso transmitted on the DL shared control channel 115 from the eNodeB110 to the WTRU 105. The UL shared control channel 140 is used to sendcontrol information from WTRU 105 to the eNodeB 110. From the controlsignaling received on the DL shared control channel 115, the WTRU 105receives information as to the physical resources that are allocated. AUL shared data channel 145 is used to transmit data from the WTRU 105 tothe eNodeB 110. After receiving UL packets from the WTRU 105, the eNodeB110 then transmits H-ARQ feedback (ACK/NACK) 150 to the WTRU 105.Furthermore, the eNodeB 110 transmits a CQI 155 to the WTRU 105 based onthe measurement and estimation of at least one UL reference channel 160that is transmitted from the WTRU 105 and received by the eNodeB 110.

The eNodeB 110 continuously determines whether an in-synchronizationstatus or an out-of-synchronization status is detected, and reports theresults through a signaling message. A higher layer component isconfigured to preferably declare an RL failure based on appropriatecriteria and associated timers and counters only when an out-ofsynchronization status is detected. Preferably, the MAC layer componentof the MAC layer component of the eNodeB 110 is configured to determinewhether an in-synchronization status or an out-of-synchronization statusis detected. Quantities used for estimation for the UL RL failuredetection are discussed below and are preferably based on thecharacteristics of the LTE UL channel structure.

Due to the new characteristics of LTE UL channel structure, some newquantities have to be used for estimation for the UL RL failuredetection. These quantities may not be exactly the same as those usedfor DL RL failure detection.

At the eNodeB 110, the information contained in the UL shared controland data channels is used as the estimation quantities of the UL RLfailure detection. Specifically, the UL thin channel is used to providea periodic and/or temporarily allocated link in UL. Thus, the newcriteria and parameters for UL RL failure detection may include one ormore of the following:

-   -   1) whether a reported CQI is below a certain threshold Q_(UL)        _(—) _(CQI) within a specified period T_(UL) _(—) _(CQI) sliding        window average).        -   1a) whether a CQI to be reported to WTRU (measured from UL            reference channel) is below a specified threshold Q_(UL)            _(—) _(CQI) within certain period T_(UL) _(—) _(CQI);        -   1b) whether a CQI from feedback from WTRU (measured on the            DL reference channels transmitted from the eNodeB) is below            a specified threshold Q_(DL) _(—) _(CQI) within a certain            period T_(DL) _(—) _(CQI); and        -   1c) a combination of CQI for both UL and DL.    -   2) Rate Request reception—whether a predefined periodic or        polled UL timing synchronization signal is not received for a        specified period T_(UL) _(—) _(Thin).    -   3) UL Data Reception        -   3a) whether no response to the scheduling grants are            received for a specified period T_(UL) _(—) _(Resp) _(—)            _(ULGrant); and        -   3b) whether ACK/NACK ratio and/or discarded DL transmissions            is below a specified threshold R_(UL) _(—) _(ACK).    -   4) UL Data BLER—calculated by ACK/NACK ratio on final data        transmission attempt from the WTRU's UL shared data channel.    -   5) UL Resource Grant    -   Allocated UL resources cannot guarantee the SRB bit rate, and        timeout following no response to multiple resource requests.    -   6) UL Control Reception—whether the quality of a UL shared        physical channel is below certain threshold Q_(UL) _(—) _(SIR),        Q_(UL) _(—) _(BLER) (SIR, EbNo, CRC/BLER, and the like) over a        specified time period T_(UL) _(—) _(SIR), T_(UL) _(—) _(BLER).

A higher layer should determine the subset of the above quantities andwhat the appropriate thresholds, timers, counters and parameters (asdescribed above) to be used for UL RL status detection should be. Thefollowing parameters should be configured to support the UL RL failure:

1) Estimation quantities and parameters to be used for UL RL failuredetection;

2) Specific timer duration for each quantity and special parameter; and

3) Specific counters for each quantity and special parameter. Thesignaling for UL RL failure detection can be the UL RL failureindication.

The eNodeB can begin the UL RL detection process once the eNodeB isconfigured with above information. Similar to described above for WTRU,the high level procedure can be proposed in two embodiments dealing withthe Keep Alive (using thin channel) and Non-Keep Alive (without usingthin channel) cases.

FIG. 3A is a signaling diagram depicting a UL RL failure detectionprocedure in a wireless communication including a WTRU 105 and an eNodeB110 in accordance with the present invention. As shown in FIG. 3A, a CQIis measured from a UL reference channel and is reported by the WTRU 105.The UL RL failure detection may detect the failure of a UL rate request,(a thin UL channel or a non-synchronous random access channel (RACH)), aUL shared control channel, a UL shared data channel or a UL resourcegrant.

In accordance with a third embodiment of the present invention, a keepalive channel scenario of SRBs is implemented as follows:

1) Since there is a pre-defined UL thin channel maintained for SRB inthis scenario, it is proposed to measure the channel quality on UL thinchannel as a main factor to estimate the quality for UL SRBtransmission. The DL thin channel may be used to probe, (i.e., “ping”),for RL failure. It may probe based on criteria similar to those used todetermine UL RL failure.

2) Other estimation quantities can be used as a complimentary approachto assist the UL RL failure detection. Exact quantities and parametersshould be configured before the start of the detection procedure.

3) If the configured estimation quantities are not meeting certainthresholds within a pre-configured time period, then UL RL failure isdetected and it should be declared, then:

-   -   a) The eNodeB should signal the failure status to WTRU;    -   b) The eNodeB should take the necessary actions for UL RL        recovery; and    -   c) The eNodeB should reset the timers and counters for new        detection.

In accordance with a fourth embodiment of the present invention, a highlevel UL RL detection procedure for a non-keep alive channel scenario ofSRBs is implemented.

1) In this case, there is no pre-allocated UL thin channel for SRBservice. Although there are other periodic UL receptions, such as a ULreference channel, these are not directly related to the UL SRBtransmission, so they can only be used by combining with otherquantities, especially the shared data channel transmitting the UL SRBs.

2) The following procedures are similar as described in step 3) of thethird embodiment.

Estimation quantities described above can be used to assist the UL RLfailure detection. Exact quantities and parameters (part of or all ofthem) should be configured before the start of the detection procedure.

If the configured estimation quantities are not meeting certainthresholds within a pre-configured time period, then UL RL failure isdetected and it should be declared, then:

-   -   a) The eNodeB should signal the failure status to WTRU;    -   b) The eNodeB should take the necessary actions for UL RL        recovery; and    -   c) The Node-B should reset the timers and counters for new        detection.        The gap due to discontinuous reception (DRX)/discontinuous        transmission (DTX) should be handled properly while setting the        timer or measurements.

FIG. 3B is a flow diagram of a method 300 for detecting uplink radiolink failure. In step 305, the channel quality of a UL thin channel ismeasured if there is a pre-allocated UL thin channel maintained for anSRB to estimate the quality for UL SRB transmission. In step 310,quantities and parameters are configured for performing UL RL failuredetection. If an UL RL failure is detected and declared in step 315, aneNodeB signals UL RL failure status to a WTRU in step 320. The eNodeBthen performs necessary actions for UL RL recovery in step 325 and theeNodeB resets timers and counters for new RL failure detection in step330.

The present invention may be implemented in any type of wirelesscommunication system, as desired. By way of example, the presentinvention may be implemented in any type of LTE, OFDM-MIMO or any othertype of wireless communication system. The present invention may also beimplemented in software, DSP, or on an integrated circuit, such as anapplication specific integrated circuit (ASIC), multiple integratedcircuits, logical programmable gate array (LPGA), multiple LPGAs,discrete components, or a combination of integrated circuit(s), LPGA(s),and discrete component(s).

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention. Themethods or flow charts provided in the present invention may beimplemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

1. A method, implemented by a wireless transmit/receive unit (WTRU), ofdetermining a radio link (RL) synchronization status, the methodcomprising: determining a quality of a downlink (DL) common sharedcontrol physical channel communicated in a channel structurecorresponding to a long-term evolution (LTE) compatible network;comparing the quality to a predetermined threshold; and determining theRL synchronization status, based at least in part, on the comparison. 2.The method of claim 1, wherein the quality is based, at least in part,on a period of time.
 3. The method of claim 1, wherein the RLsynchronization status is determined to be out-of-synchronization uponthe comparison indicating an out-of-synchronization condition.
 4. Themethod of claim 1 wherein the quality of the downlink (DL) common sharedcontrol physical channel is monitored on at least one of a continuousbasis or a periodic basis.
 5. The method of claim 3, further comprisingindicating the out-of-synchronization status to at least one logicallayer in communication with a physical layer.
 6. The method of claim 5further comprising: transmitting a channel quality indicator (CQI) basedon at least one of a measurement or estimation of at least one DLreference channel received by the WTRU.
 7. The method of claim 5 furthercomprising: receiving a channel quality indicator (CQI) based on atleast one of a measurement or estimation of at least one uplink (UL)reference channel.
 8. A wireless transmit/receive unit (WTRU configuredto: determine a quality of downlink (DL) common shared control physicalchannel communicated in a channel structure corresponding to a long-termevolution (LTE) compatible network; compare the quality to apredetermined threshold; and determine an RL synchronization status,based at least in part, on the comparison.
 9. The WTRU of claim 8wherein the WTRU is configured to transmit a channel quality indicator(CQI) based on at least one of a measurement or estimation of at leastone downlink (DL) reference channel received by the WTRU.
 10. The WTRUof claim 8 wherein the RL synchronization status is determined to beout-of-synchronization upon the comparison indicating anout-of-synchronization condition.
 11. The WTRU of claim 8 wherein thequality is monitored on at least one of a continuous or periodic basis.12. The WTRU of claim 10 further configured to indicate that theout-of-synchronization status has been detected to a logical layer incommunication with a physical layer.
 13. The WTRU of claim 12, whereinthe WTRU is configured to transmit a channel quality indicator (CQI)based on at least one of a measurement or estimation of at least one DLreference channel received by the WTRU.
 14. The WTRU of claim 12 whereinthe WTRU is configured to receive a channel quality indicator (CQI)based on at least one of a measurement or estimation of at least oneuplink (UL) reference channel.
 15. The WTRU of claim 8 wherein thequality is based, at least in part, on a period of time.